In an ink-jetting recording head, which is an example of a liquid jetting head, a plurality of pressure-chambers are formed in the same substrate into one or more rows so as to communicate with respective independent nozzles and a common ink-chamber. A drop of ink can be jetted from a nozzle when the volume of a pressure-chamber corresponding to the nozzle is changed by a piezoelectric vibrating member and so on, or when the ink in the pressure-chamber is vapored by a heating element.
The pressure-chambers of the ink-jetting recording head have to be formed at regular intervals (pitches) corresponding to desired recording density. Thus, the pressure-chambers are formed by an etching process of a metal substrate or by an injection molding of a polymer material.
In order to ensure a high etching accuracy, it is effective to conduct an anisotropic etching process by using a silicon single crystal as a substrate material. However, in the case, there is a problem of increase of material cost.
On the other hand, in a case wherein an injection molding of a polymer material is conducted, the pressure-chambers can be relatively easily formed with higher accuracy. However, no polymer material has high rigidity, so that the pressure-chambers formed therein tend to be deteriorated by means of driving of the piezoelectric vibrating members or heat generation of the heating elements.
In order to solve the above problems, an invention described in Japanese Patent Laid-Open Publication No. 2000-263799, which was filed by the applicant, provides an ink-jetting recording head superior in durability and manufacturing cost.
In the invention disclosed in the above gazette, as shown in FIG. 10, a flowing-path unit is formed by layering: a nozzle plate 103 through which a plurality of nozzles 102 are formed; a flowing-path substrate 108 having a plurality of pressure-chambers 105 communicating with the plurality of nozzles 102, a reservoir 107 for supplying ink through a plurality of ink-supplying ports 106 to the plurality of pressure-chambers 105, a first surface 108a and a second surface 108b opposite to the first surface 108a; and a lid plate 111 that seals the first surface 108a of the flowing-path substrate 108. A piezoelectric vibrating member is provided to increase a pressure of the ink in each pressure chamber 105. A through hole that becomes the reservoir 107 is formed through a metal plate having the first surface 108a and the second surface 108b, that is, from the surface 108a to the second surface 108b. Then, a plurality of concave portions that become the plurality of pressure-chambers 105 are formed on the first surface 108a of the metal plate by a press working, so that the flowing-path substrate 108 is formed.
According to the invention disclosed in the gazette of Japanese Patent Laid-Open Publication No. 2000-263799, the flowing-path substrate 108 is formed by a press working from a metal plate such as a nickel plate or the like, which is superior in extensibility. This working way is simple and cheap.
FIG. 1 shows an electric circuit equivalent to an ink-jetting recording head. In FIG. 1, m[kg/m4] represents inertance, c[m5/N] represents acoustic capacitance, r[Ns/m5] represents acoustic resistance, and U[m3/s] represents volume velocity. Regarding indices thereof, the index “0” means a vibrating member system including a piezoelectric member (laminated PZT) and a vibrating plate connected thereto, the index “1” means an ink pressure-chamber system, the index “2” means an ink supplying flowing-path system, and the index “3” means a nozzle flowing-path system. The contents of the brackets [ ] represent respective units.
When the equivalent electric circuit is broken up, a circuit including only the vibrating member system shown in FIG. 2 can be extracted. The circuit has a natural period depend on the vibrating member, which may be represented by the following expression.Ta=2π√{square root over (m0c0)}  (1)
In addition, when the equivalent electric circuit shown in FIG. 1 is broken up, a circuit consisting of the ink pressure-chamber system, the ink supplying flowing-path system and the nozzle flowing-path system can be extracted, as shown in FIG. 3. In the circuit, as viewed from the ink pressure-chamber, the nozzle flowing-path system and the ink supplying flowing-path system are connected in parallel. In addition, the circuit has a natural period of the ink flowing-path system, which may be dominated by the acoustic capacitance of the ink pressure-chamber and may be represented by the following expression.                               T          c                =                  2          ⁢          π          ⁢                                                                      m                  2                                ·                                  m                  3                                                                              m                  2                                +                                  m                  3                                                              ⁢                      c            1                                              (        2        )            
In addition, when the equivalent electric circuit shown in FIG. 1 is broken up, a series circuit consisting of the nozzle flowing-path system and the ink supplying flowing-path system can be extracted, as shown in FIG. 4. The circuit has a natural period of the ink flowing-path system, which may be dominated by the acoustic capacitance by surface tension of an ink meniscus formed in the nozzle and may be represented by the following expression.Tm=2π√{square root over ((m2+m3)c3)}  (3)Herein, the above natural periods are different and away from each other, and the following expression is satisfied.Ta<Tc<Tm  (4)
In addition, the inertance m of the ink flowing-path system is calculated by the following expression.                     m        =                  κ          ⁢                      ∫                                          ρ                S                            ⁢                              ⅆ                x                                                                        (        5        )            Herein, ρ represents an ink density, S represents a sectional area of the flowing-path perpendicular to a flowing direction of the ink, x represents a coordinate in the flowing direction, and κ is a coefficient depend on a vibration (oscillation) frequency of the ink flow. For example, the value of κ is 1.4.
It is preferable that ink-jetting control of an ink-jetting recording apparatus is conducted to a plurality of nozzles in a common manner. For that purpose, it is requested that characteristics of the plurality of nozzles, in particular frequency response characteristics of the plurality of nozzles, coincide with each other.
In general, ink is supplied from a common ink chamber to a plurality of pressure-chambers respectively communicating with a plurality of nozzles. If the plurality of nozzles are aligned on a line segment, a substantial sectional area S of an ink flowing-path from the common ink chamber to a pressure-chamber communicating with a nozzle in the vicinity of an end of the line segment is smaller than a substantial sectional area S of an ink flowing-path from the common ink chamber to a pressure-chamber communicating with a central nozzle away from the end of the line segment, because of effect of an end wall of the ink chamber. Thus, characteristics of the plurality of nozzles formed on the line segment may be different. In detail, the characteristic of a nozzle in the vicinity of the end of the line segment and the characteristic of a central nozzle away from the end of the line segment may be different.
In addition, the common ink chamber is usually formed into a tapered shape, in which a flowing-path width thereof is positively tapered, in an area in the vicinity of the end wall, in order to raise a flowing speed of the ink to prevent air bubbles from remaining when the ink is supplied (filled) or when the ink is sucked for a cleaning operation. In the case, a substantial sectional area S of an ink flowing-path from the common ink chamber to a pressure-chamber communicating with a nozzle in the vicinity of an end of the line segment becomes further smaller than a substantial sectional area S of an ink flowing-path from the common ink chamber to a pressure-chamber communicating with a central nozzle away from the end of the line segment. This may increase the possibility that the characteristic of a nozzle in the vicinity of the end of the line segment and the characteristic of a central nozzle away from the end of the line segment be different.